Regulatory Effect of Thyroxine on Calcium and Phosphorus Metabolism in Tissues of Common Indian Toad

Thyroxine (T₄) plays a vital role in the metabolic processes of animals. It influences the storage and mobilisation of minerals and their utilisation according to the requirement of the body. It is also involved in the early development of vertebrates, especially in amphibian metamorphosis. It has shown anabolic and catabolic effects at a lower dose and higher dose, respectively. The present study aims to identify the role of thyroxine in regulating calcium and phosphorous metabolism in the blood, muscle and bone tissues of Bufo melanostictus. Toads of various sizes and different age groups were chosen, showing a positive correlation between body weight and snout to vent length, indicating overall continuous growth as observed for a large number of poikilothermic animals. As per an earlier report, thyroxine has been shown to have a direct catabolic effect on bone mineral homeostasis leading to an increase in bone mineral resorption and calcium loss through the kidney. Results of the present study indicate that thyroxine treatment in Bufo melanostictus caused depletion of calcium and phosphorous in muscle and bone, while their level increased in the serum at both doses (0.5 μg/gm and 2 μg/gm) during short term i.e. a one-day T₄ treatment. Such results are very much consistent with many of the earlier obscurations that, T₄ causes an increase in serum calcium and phosphorous levels, while their level in muscle and bone decreased. When the level of these two minerals falls in the serum due to any other condition, the bone resorption under the influence of thyroxine maintains the concentration in serum, consequently, there is a loss in bone density due to resorption and in muscle due to utilisation. However, if the exogenous supply is adequate, the loss caused as above is compensated for, in both bone and muscle.